Ammonia inhibition of the maximum growth rate (?m) of hydrogenotrophic methanogens at various pH-levels and temperatures

Abstract

A method for the quantitative measurement of the maximum growth rate (μm) of hydrogen-consuming methanogenic populations was applied to assess the toxicity of ammonia1 under various pH and temperature conditions. The maximum uninhibited growth rate of the hydrogenotrophic population present in sludge from an industrial anaerobic wastewater treatment system appeared to be 0.126 h-1 at pH=7 and 37°C. At 350 mM ammonia the maximum growth rate had decreased to almost half that value. At a temperature of 29°C the maximum growth rates in the ammonia range tested appeared to be approximately 60% of that at 37°C, while increasing ammonia concentrations caused a similar maximum growth rate decline. At 37°C an increase of the pH to 7.8 appeared to enhance ammonia inhibition of the maximum growth rate. Increased propionate concentrations (tested up to 60 mM) appeared to have no effect on ammonia inhibition.